This bug is awaiting verification that the kernel in -proposed solves
the problem. Please test the kernel and update this bug with the
results. If the problem is solved, change the tag 'verification-needed-
disco' to 'verification-done-disco'. If the problem still exists, change
the tag 'verification-needed-disco' to 'verification-failed-disco'.

If verification is not done by 5 working days from today, this fix will
be dropped from the source code, and this bug will be closed.

See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how
to enable and use -proposed. Thank you!


** Tags added: verification-needed-disco

** Tags added: verification-needed-xenial

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https://bugs.launchpad.net/bugs/1833410

Title:
  idle-page oopses when accessing page frames that are out of range

Status in linux package in Ubuntu:
  In Progress
Status in linux source package in Xenial:
  Fix Committed
Status in linux source package in Bionic:
  Fix Committed
Status in linux source package in Cosmic:
  Fix Committed
Status in linux source package in Disco:
  Fix Committed

Bug description:
  == SRU [Xenial][Bionic][Cosmic][Disco] ==

  == Justification ==

  When accessing page frames that are greater than max_pfn using the
  idle-page sysfs interface an oops is triggered that kills the process
  that writes to the sysfs interface.

  == Fix ==

  Upstream fix currently in linux-next:

  https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-
  next.git/commit/mm/page_idle.c?id=d96d6145d9796d5f1eac242538d45559e9a23404

  This fixes the maximum pfn threshold allowed.

  == Test ==

  sudo stress-ng --idle-page 0

  this should trigger the oops in ~50% of the cases due to the way the
  threshold calculation in the kernel was handling the maximum threshold
  based on pfn alignments. 31 of 63 of the times it may be under the
  threshold so no oops occurs.  If it does not, increase or decrease the
  number of available pages in a system to trigger the sweet spot of the
  bug.

  == Regression Potential ==

  Minimal, this touches a sysfs kernel interface that is not used much.
  The fix narrows the scope of touching specific page frames, so the
  page frame scope is reduced by the fix.

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